This invention relates to communication systems, such as mobile communications and in particular but not exclusively to the GSM Public Land Mobile Network (PLMN).
The term GSM refers to the standards for pan-European mobile cellular radio telephony systems at 900 MHz defined by a CEPT standards group called Groupe Speciale Mobile. This has been adopted by ETSI and GSM has come to represent Global Systems for Mobile Communication. A basic GSM network architecture is illustrated schematically in FIG. 1. The GSM network basically comprises a base-station system (BSS) which includes a base-station controller (BSC) and one or more base-station transceiver stations (BTS), associated with each mobile services switching center (MSC) (only one BSC is illustrated), a home location register (HLR) and a visitors location register (VLR). Every subscriber (mobile station MS) is allocated to a home network, and possibly an MSC within that network, this being achieved by making an entry in the HLR. Whenever a mobile is switched on and at regular intervals thereafter, it will register with the system and give its location area (group of cells). If the mobile is not in its home area, the subscriber's data will be added to the VLR of the then local MSC. The MCSs attend to the routing of calls to their destinations, each MSC being connected to other MSCs, and Gateway MSCs (GMSC) having interfaces for connection to PSTNs (Public Switched Telephone Networks) and other service providers, and network management etc. functions (NMC, OMC).
The key network principles of GSM are standardisation of network components; the separation of network components by standard interfaces; a network infrastructure based on the Intelligent Network (IN) principles of centralised databases which contain all information about subscribers in the network; and the use of a common radio interface based on ISDN signalling capabilities to provide advanced voice and data services.
The HLR is a central component in the IN infrastructure of the GSM PLMN. It is a centralised database which contains subscription information, service activation information and current location information for each subscriber within the network. There are two other centralised databases, the Authentication Center (AUC) and the Equipment Identification Register (EIR). The AUC provides the keys for maintaining the security of subscribers' identities and for encrypting information passed over the air interface, whereas the EIR is used to control access to the network by unapproved, stolen or faulty mobile stations. The AUC may be considered to be part of an HLR which provides both HLR and AUC functioning, as may the EIR be so considered. The information contained within the HLR allows a mobile subscriber to be addressed by a unique directory number independent of geographical location. Thus, mobile stations are able to roam freely within networks and from one network to another. The HLR handles transactions with both the MSC and the VLR, which either request information from the HLR, or update the information currently held in the HLR. The HLR also initiates transactions with the VLR to complete incoming calls and update subscriber data.
As mentioned basic GSM operates at 900 MHz, however, there are other mobile telephony systems based on GSM standards but implemented at the 1.7-2.3 GHz range. Personal Communication Networks (PCN) are one such system and are known as DCS 1800 (Digital Cellular System at 1800 MHz). The HLR with which the present invention is concerned is applicable to GSM and PCN and also to other mobile systems which are not GSM based.
The HLR is the central point within the network upon which all call routing and service delivery depends. The GSM network cannot serve subscribers without an HLR since the HLR contains the subscriber provisioning information. The network cannot terminate any calls without the HLR since it contains the location information. The MSC cannot offer more subscriber services than those which are provisioned within the HLR as there is no mechanism by which to provide the subscription information to the MSC other than via the HLR.
In the case of a small network, i.e. one with few subscribers, an HLR database having a single query processor can suffice. The HLR database is connected to the MSC and the rest of the network through a Signalling System such as a CCS7 signalling network. The single processor contains all of the subscribers' subscription information (permanent data PD) and also all of the temporary information (TD) relating to service activation and current location. The HLR provides the network with facilities for examining the permanent data (PD) and examining and modifying the temporary data (TD). These facilities are provided as Network Functions which are realised as sequences of messages. The network functions which are provided by the HLR include the following, (no specific details are given since they are specified in GSM, for example): Incoming Call Handling; Outgoing Call Handling; Supplementary Services Management; Location Registration; Authentication; Registration; Subscriber Management and Short Message Service Handling. Queries from an MSC can be fed serially into the single processor when the system is small (small number of subscribers). As the system grows and the number of subscriber increases more than one query processor (QP) will be required, and each will not be able to handle all of the PD and TD, hence each QP will only have limited information, such as that relating to the PD and TD of a particular group of subscribers. In this case, means such as a central clearing house will need to precede the QP's so that the relevant QP can be addressed for each query. With further growth in the number of subscribers, the central clearing house approach results in an unacceptable processing bottleneck, since all queries must be routed through it. An alternative would be to have more than one central clearing house i.e. more than one HLR, however this then involves changes to the method by which individual subscribers are identified, in particular all of the subscribers IMSI (International Mobile Subscribers Identity) numbers would need to be changed. The IMSI is a radio path subscriber identity (of up to 15 digits) which is used during signalling transactions between the mobile station and the fixed network to identify uniquely each mobile subscriber. It is formatted as Home Country Code (CC)+PLMN Code+HLR Code+Subscriber Number in the HLR SI. The Mobile subscriber may also be identifiable through another key, such as the Mobile Subscriber Integrated Services Digital Network (MSISDN) number. Each mobile subscriber then has an IMSI through which it is uniquely identifiable together with, for example, a number of MSISDN numbers, each of which provides access to the mobile subscriber for a specific type of call (voice, fax, etc.) All MSISDN numbers associated with a mobile subscriber are resolved to its IMSI within the HLR. This information is loaded into the HLR by the service operator.
It is an object of the present invention to provide an HLR which is able to grow from a very small data base to a very large data base without involving central clearing house functions and their associated bottlenecks.